Parasit - Lab Quiz 1-1

Definitions

a. An organism that lives in or on another organism of a different species b. Metabolically dependent on the host during part or all of its life c. Usually harmful to the host

Define Parasitism

a. A kind of symbiotic relationship between two different species of organism b. One (the parasite) is metabolically dependent on the other (the host) c. Can go from essentially harmless (commensal) to highly virulent

Define Facultative parasite

An organism that is capable of living either a free or parasitic existence (like a fly. Just using the faculties!)

Define Endoparasite

A parasite that lives mainly inside the body of its host (e.g., hookworms).

Define Ectoparasite

A parasite that lives mainly on the surface of its host (e.g., fleas, ticks & lice).

Usually an arthropod (e.g., face fly); may be an intermediate host or a mechanical vector.

Define Paratenic (or Transport) host

A nonessential host, (e.g., rodents, roach), in the life cycle of a parasite capable of harboring & maintaining immature stages; parasites undergo no development or proliferation w/in these hosts, but are merely carried w/in the body until consumed by the proper definitive host.

Define Reservoir host

A population of infected hosts which serve as a potential source of infxn for other species of susceptible domestic animals or humans (e.g., wild [feral] animals).

Define Infective stage

Developmental stage of the parasite capable of initiating a new infxn w/in another host (e.g., eggs, oocysts, larvae).

Define Direct life cycle

Transmission of parasitic infxn from 1 host to another w/o the requirement of an intermediate host; 1-host life cycle.

Define Indirect life cycle

Transmission of parasitic infxn from 1 host animal to another through 1 or more essential intermediate hosts; multi-host life cycle.

Define Pre-patent period

The time between ingestion & invasions of infective stages of a helminth parasite in its definitive host until eggs or larvae are 1st produced (e.g., the time between ingestion of infective L3 nematode larvae until the appearance of eggs in the feces).

Clinical infxn by parasites characterized by slow debilitation, small to moderate parasite numbers, & clinical signs are usually slow in developing.

Define Subclinical infxn

Parasite infxn in which no clinical signs are manifested, however, evidence of parasitism may be detected by decreased growth, loss of production, etc. Many herd health parasitic problems are related to subclinical infxns.

How do parasites injure their hosts?

They feed on blood, lymph, exudate or solid tissues; compete w/ the host for nutrition; they cause mechanical obstruction; they may produce pressure atrophy; destroy host cells by growing in them; they may produce toxic substances; they may produce host allergic rxns; they may promote the neoplastic transformation of cells; they may be biological vectors or intermediate hosts; contribute to decreasing the host’s immune system.

Protozoa are __cellular, __karyotic organisms

Unicellular, eukaryotic (have true nucleus)

What are the 2 life stages of protozoa?

Trophozoite & cyst

Describe the trophozoite life stage

Motile feeding form – very fragile & may be free-living or the infective stage (depending on the protozoan)

Binary fission Budding Multiple fission or Schizogony (a form of asexual reproduction characteristic of certain protozoa, including sporozoa, in which daughter cells are produced by multiple fission of the nucleus of the parasite (schizont) followed by segmentation of the cytoplasm to form separate masses around each smaller nucleus.)

MALE- asymptomatic. FEMALE- EARLY ABORTION!! 3-4mo. Also might have varying degrees of vaginitis, cervicitis, salpingitis, & placentitis. Often endometritis w/ purulent discharge that may lead to sterility – infected cows are often restless

Bulls: infected should NOT be used as breeding animals → prognosis for clearing of the chronically infected is guarded(treatment involves intensive flushing of prepucial cavity with 6 confirmed negative culture before returning to breeding)Cows: vaccine is currently available = TrichGuardTM for cows(previously infected should be artificially inseminated for at least 2 years following diagnosis with sexual rest of the cow for 2-6 months)

Describe the life stages of Tritrichomonas foetus

Trophozoite stage, NO CYST STAGE!

Describe the appearance of the trophozoite stage of tritrichomonas foetus

DIRECT, but unique, bc it is a pleomorphic protozoan (shape depends on where it is in the body). AMOEBOID STAGE- found in cecum, & after hepatic invasion. TRANSITIONAL FORM- present in intestinal lumen (NO CYST STAGE)

What is the route of transmission for histomonas meleagridis?

Fecal-oral, Direct, but Unique. Earthworms or Nematodes (Heterakis gallinarum) serve as a (paratenic hosts) that the bird (definitive host) ingests. The Heterakis eggs (cecal worm eggs) containing the Histomonas passes through into the bird's feces. Through fecal-oral transmission, the ingested Heterakis eggs that contained the Histomonas that was in the feces is now passed once again, but now the egg can hatch in the cecum where the Histomonas is finally liberated. The flagellated form of the Histomonas develops here in the cecal lumen. When this form gets exposed to outside temperatures, it dies rapidly as a result without the protection of the nematode's egg shell.

How is histomonas meleagridis transmitted?

Infxn occurs when direct host (chicken) eats the eggs of the cecal worm, which carry histomonas inside of them. This is bc histomonas uses the parasetic host to survive outside. Adult cecal worms in the host ingest Histomonas, which then pass into the worm eggs w/in the DH, allowing Histomonas to “hitch a ride” to the outside world in the resistant nematode egg shell

1. Based on clinical signs and presence of liver and cecal lesions 2. ELISA and PCR can confirm diagnosis

Describe the appearance of histomonas meleagridis

1. Pleomorphic (the ability to alter their shape or size in response to environmental conditions) 2. Amoeboid Form (a. Found in the intestinal lumen (1 or 2 flagella)b. In tissues it is found singly or in clusters (Flagellum is absent) ) 3. Transitional Forms(a. May be present in the lumenb. Enclosed in a dense membranec. Both lumen and intestinal forms die rapidly when exposed to outside temperature) 4. No evidence of a cyst stage(a. Has been produced experimentally in tissue culture)